In the field of spark ignited engines, a loss of electric power necessarily results in a cessation of spark and correspondingly, the engine discontinues operation. For example, operation of the key switch in an automobile to the "off" position interrupts electric power causing the engine to stop. However, there are a group of engines (e.g., diesel, turbine, etc.) whose continued operation is independent of the electric system. That is to say, after a suitable starting period the combustion process is self sustaining and absent mechanical failure, the continued supply of fuel will maintain the engine in an operating mode.
From this description it becomes obvious that one method of operator intervention for shutting down an engine would be to discontinue the supply of fuel. There are two well established methods of providing this function, both of which employ an electrically operated solenoid to actuate the rack of the fuel system to a detent position, where the fuel supply is interrupted. The electric solenoid provides a means for shutting down the engine which appears similar to the well accepted method employed by the automotive industry, where operation of the ignition switch to the "off" position shuts down the engine.
The first of these methods uses what is called an energized to run solenoid. Electric power is continuously supplied to the solenoid while operation of the engine is desired, allowing the supply of fuel to continue. At such time as when the operator desires to shut down the engine, deactivating the key switch shuts off power to the solenoid which discontinues the supply of fuel. Clearly, this system does have some inherent disadvantages. For example, in the operation of construction equipment, an electrical failure for any reason results in the engine being shut down with no capability for restarting or driving the vehicle to a service area. Additionally, constant energization during operation requires that the solenoid be constructed more ruggedly than a solenoid which is actuated intermittently. A constantly energized solenoid would require more heat dissipation and inductive coils capable of carrying current for longer periods of time and withstanding additional heat.
The second method employs a system called an energized to shut down solenoid. This system supplies electric power to a solenoid for a predetermined amount of time upon deactivating the key switch. Energizing the solenoid results in the fuel supply being shut off for a predetermined amount of time to insure that the engine has been shut down. While this system overcomes the disadvantages associated with constantly energized solenoids, it does suffer from problems unique to its own construction. For example, loss of electric power does not provide the operator with the ability to shut down the engine and the actuation of the solenoid for a predetermined amount of time does not assure that the engine is shut down. Additionally, the electrical circuitry required to provide power for a predetermined time period has proven to be a costly addition.
The present invention is directed to overcoming one or more of the problems as set forth above.